This invention relates to a signal transmission system over building or house wiring and more particularly to a noise reduction circuit in such a signal transmission system.
It is known in the art of signal transmission that, in a transmission system of the type which utilises building or house wiring for power distribution, digital data included in carriers are transmitted and received via indoor power lines in synchronism with the utility power frequency for building security or other purposes. For such system, it is necessary to remove any kind of noise from the carriers prior to proper treatment of signals. There are generally two kinds of noise, asynchronous noise (i.e., random noise) and synchronous noise (i.e., thryristor noise).